1. Technical Field
This disclosure relates to a piezoelectric actuator, a liquid ejection head, and an image forming apparatus.
2. Description of the Background Art
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities. As one type of image forming apparatuses are known inkjet-type image forming apparatuses (inkjet recording apparatus) using a recording head formed with a liquid ejection head (liquid-droplet ejection head). During image formation, such inkjet-type image forming apparatuses eject droplets of ink or other liquid from the recording head onto a recording medium to form a desired image.
Such inkjet-type image forming apparatuses fall into two main types: a serial-type image forming apparatus that forms an image by ejecting droplets from the recording head while moving the recording head in a main scanning direction of the carriage, and a line-head-type image forming apparatus that forms an image by ejecting droplets from a linear-shaped recording head held stationary in the image forming apparatus.
As the liquid ejection head, for example, a piezoelectric head like that described in JP-08-142325-A is known that includes a piezoelectric member serving as a pressure generator to press ink in liquid chambers to generate pressure to the ink, in particular, a piezoelectric actuator having a plurality of pillar-shaped piezoelectric elements (piezoelectric pillars) formed by groove-processing a laminated piezoelectric member in which piezoelectric layers and internal electrodes are alternately laminated. The laminated piezoelectric elements are deformed in the d33 or d31 direction to deform elastic diaphragms. As a result, the internal volume and pressure of liquid chambers are changed to eject liquid droplets.
In a piezoelectric actuator used in a conventional liquid ejection head like that described in JP-3546430, for example, the width of a plurality of piezoelectric pillars in a direction perpendicular to a direction in which the piezoelectric pillars are arrayed is greater at an upper side than at a bottom (lower) side.
For such image forming apparatuses, downsizing of liquid droplets and increasing of the nozzle array density have been made to obtain high-quality images. Further, to enhance the image formation speed, the driving frequency of the liquid ejection head has been increased or the length of the liquid ejection head has been increased with an increased number of nozzles per head as in line-type liquid ejection heads.
To produce such a highly-integrated head, it is preferable that, in the formation of multiple piezoelectric pillars, the width of the piezoelectric pillars in the direction in which the piezoelectric pillars are arrayed (hereinafter, the term “width” represents a width in the above-mentioned direction), the pitch of grooves processed, and the width of grooves are small while the depth of the grooves (the height of the piezoelectric pillars) is great so as to form a high aspect ratio. However, in such a case, the piezoelectric pillars may be inclined in the groove processing.
To prevent such inclination of piezoelectric pillars, it is conceivable to increase the width of piezoelectric pillars to enhance the hardness of piezoelectric pillars. However, in such a configuration, a relatively-thin blade need be used in groove processing, thus requiring an increased hardness of the blade. By contrast, if a thick blade is used, the width of piezoelectric pillars becomes small. However, in such a case, the hardness of piezoelectric pillars may be insufficient, causing the inclination of piezoelectric pillars. Further, such insufficient hardness of the piezoelectric pillars may cause a reduced performance of actuators.
In addition, the more the bonded area between the piezoelectric pillars and the diaphragms (deformation members) deformed by the piezoelectric pillars, the more tolerant the actuator to misalignment of the bonded area, thus obtaining enhanced reliability. Further, the more the bonded area between the piezoelectric pillars and the diaphragms, the greater deformation force can be applied to the diaphragms. Accordingly, even if multiple nozzles are arrayed at high density, it is preferable to obtain a large bonded area between the piezoelectric pillars and the diaphragms.